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Presents a study that examined the piezoelectric properties and elastic constants of 4H and 6H silicon carbide crystals. Methodology; Correlation between the elastic constants and the temperature; Determination of the resonance frequency of the crystals.

Presents a study which investigated the elastic properties of zinc oxide (ZnO) films by means of the Brillouin scattering technique. Geometry of the interaction between impinging photons and surface phonons; Dispersion curves for Rayleigh-type acoustic modes propagating on a ZnO film; Causes of small changes in the phase velocity of ZnO films.

Focuses on a study which investigated the compositional dependence of dynamic Young's modulus and internal friction in Al[sub2]O[sub3]-3Y-ZrO[sub2] composites. Variation in internal friction; Composition dependence of the fraction of monoclinic phase; Results and discussion.

Presents a study which evaluated the elastic field induced by an edge dislocation located inside a lamellar inhomogeneity. Information on the lamellar inhomogeneity; Solution to the elastic problem; Conclusion.

Presents a study that examined the magnetoelasticity in cobalt-chromium alloy thin films. Analysis of the ferromagnetic resonance of the thin films; Evaluation of the effective anisotropy field of the sample; Correlation between stress-induced anisotropy and substrate temperature.

The effects of hydrostatic pressure and biaxial strains on the elastic and electronic properties of a superhard material t-C8B2N2 have been studied using first-principles calculations. The structure is proven to be mechanically and dynamically stable under the applied external forces. All the elastic constants (except C66) and elastic modulus increase (decrease) with increasing pressure and compressive (tensile) biaxial strain εxx. A microscopic model is used to calculate the Vicker's hardness of every single bond as well as the crystal. The hardness of t-C8B2N2 (64.7 GPa) exceeds that of c-BN (62 GPa) and increases obviously by employing pressure and compressive εxx. Furthermore, the Debye temperature and anisotropy of sound velocities for t-C8B2N2 have been discussed. t-C8B2N2 undergoes an indirect to direct bandgap transition when εxx > 2%; however, the indirect bandgap character of the material remains under pressure. [ABSTRACT FROM AUTHOR]

The effects of hydrostatic pressure and biaxial strains on the elastic and electronic properties of a superhard material t-C8B2N2 have been studied using first-principles calculations. The structure is proven to be mechanically and dynamically stable under the applied external forces. All the elastic constants (except C66) and elastic modulus increase (decrease) with increasing pressure and compressive (tensile) biaxial strain εxx. A microscopic model is used to calculate the Vicker's hardness of every single bond as well as the crystal. The hardness of t-C8B2N2 (64.7 GPa) exceeds that of c-BN (62 GPa) and increases obviously by employing pressure and compressive εxx. Furthermore, the Debye temperature and anisotropy of sound velocities for t-C8B2N2 have been discussed. t-C8B2N2 undergoes an indirect to direct bandgap transition when εxx > 2%; however, the indirect bandgap character of the material remains under pressure. [ABSTRACT FROM AUTHOR]

We report measurements of the mechanical properties of two suspended graphene membranes in the temperature range of 80 K to 550 K. For this entire range, the resonant frequency and quality factor of each device were monitored continuously during cooling and heating. Below 300 K, we have additionally measured the resonant frequency's tunability via electrostatic force, and modeled this data to determine graphene's tension and elastic modulus; both of these parameters are found to be strongly temperature-dependent in this range. Above 300 K, we observe a resonant frequency (and therefore tension) minimum near room temperature. This suggests that the thermal expansion coefficient is positive for temperatures below roughly 315 K, and negative for higher temperatures. Lastly, we observe a large, reproducible hysteresis in the resonant frequency as our graphene devices are cycled between 300 K and 550 K. After returning to 300 K, the measured frequency evolves exponentially in time with a time constant of ∼24 h. Our results clash with expectations for pristine graphene membranes, but are consistent with expectations for composite membranes composed of graphene coated by a thin layer of polymer residue. [ABSTRACT FROM AUTHOR]

Acoustic and elastic metamaterials are media with a subwavelength structure that behave as effective materials displaying atypical effective dynamic properties. These material systems are of interest because the design of their sub-wavelength structure allows for direct control of macroscopic wave dispersion. One major design limitation of most metamaterial structures is that the dynamic response cannot be altered once the microstructure is manufactured. However, the ability to modify wave propagation in the metamaterial with an external stimulus is highly desirable for numerous applications and therefore remains a significant challenge in elastic metamaterials research. In this work, a honeycomb structure composed of a doubly periodic array of curved beams, known as a negative stiffness honeycomb (NSH), is analyzed as a tunable elastic metamaterial. The nonlinear static elastic response that results from large deformations of the NSH unit cell leads to a large variation in linear elastic wave dispersion associated with infinitesimal motion superposed on the externally imposed pre-strain. A finite element model is utilized to model the static deformation and subsequent linear wave motion at the pre-strained state. Analysis of the slowness surface and group velocity demonstrates that the NSH exhibits significant tunability and a high degree of anisotropy which can be used to guide wave energy depending on static pre-strain levels. In addition, it is shown that partial band gaps exist where only longitudinal waves propagate. The NSH therefore behaves as a meta-fluid, or pentamode metamaterial, which may be of use for applications of transformation elastodynamics such as cloaking and gradient index lens devices. [ABSTRACT FROM AUTHOR]

Although recent advances have made it possible to manipulate electromagnetic and acoustic wavefronts with sub-wavelength metasurface slabs, the design of elastodynamic counterparts remains challenging. We introduce a novel but simple design approach to control SV-waves in elastic solids. The proposed metasurface can be fabricated by cutting an array of aligned parallel cracks in a solid such that the materials between the cracks act as plate-like waveguides in the background medium. The plate array is capable of modulating the phase change of SV-wave while keeping the phase of P-wave unchanged. An analytical model for SV-wave incidence is established to calculate the transmission coefficient and the transmitted phase through the plate-like waveguide explicitly. A complete 2π range of phase delay is achieved by selecting different thicknesses for the plates. An elastic metasurface for splitting SV- and P-waves is designed and demonstrated using full wave finite element simulations. Two metasurfaces for focusing plane and cylindrical SV-waves are also presented. [ABSTRACT FROM AUTHOR]

The article presents comments on the paper "Free transverse vibration of the fluid-conveying single-walled carbon nanotube using nonlocal elastic theory." It states that there are inconsistencies in applied forces and the handling of the governing equations. It presents mathematical models showing the governing differential equation of motion for free vibration of fluid-conveying tubes to examine transverse deflection and shear force on the cross section.

Presents information on a study which investigated the elastic properties of magnetic fluids using Mossbauer effect. Experimental details; Results and discussion; Conclusions.

Presents a correction to the article 'Elastic Properties of Polycrystals with Trigonal Crystal and Orthorhombic Specimen Symmetry,' by G.C. Johnson and H.R. Wenk.

Comments on the study published by Kanrar and Ghosh in the 1981 issue of 'Journal of Applied Physics' about the elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature. Claims on the linear dependence of the crystal alloys; Evidence on the nonlinearity of the crystal alloys; Sources of errors in the study by Kanrar and Ghosh.

Presents the results of a Brillouin scattering investigation of the elastic constants of hexagonal gallium nitride. Background to the study; Results and discussion.

Focuses on a study which examined the Hugoniot elastic limits of polymers using pressure-dependent yield criterion. Reason for the different yield criterion of polymers than other solids; Mechanism behind the increase shear strength with pressure of polymers; Significance of the findings.

Presents a study that derived a relation between the Hugoniot elastic limit (HEL) of brittle materials and their compressive strength. Significance of the Hugoniot elastic limit; Ratio between the HEL and the equivalent dynamic compressive strength; Yield surface of brittle failure.

Presents a study which performed plate-impact experiments on boron carbide specimens to measure their Hugoniot elastic limit (HEL) values. Assumption of the Steinberg model used in the study; Decrease in HEL values; Methodology used in the study; Results.

Studies the elastic constants of a cobalt disilicide intermetallic compound. Applications of cobalt disilicide intermetallic compound; Details on the experiment.

A correction to the article ""The bonding, charge distribution, spin ordering, optical, and elastic properties of four MAX phases Cr2AX (A5Al or Ge, X5C or N)" that was published in the previous issue is presented.

The flow units of glasses are generally perceived to be a local rearrangement of atoms that are microstructural origin for plastic deformation and relaxations in metallic glasses. We find a relationship of the effective concentration of flow units and some properties such as elastic moduli, micro-hardness and plasticity of metallic glasses. The relationship helps in understanding the softening phenomenon, structural heterogeneous, evolution process of flow units, and widespread mechanical behavior of metallic glasses and can reveal the essential structural mechanism of the Poisson's ratio criterion for plasticity in metallic glasses. The relationship also indicates that the flow unit is a key structural parameter for understanding and controlling the properties and the performance of metallic glasses. [ABSTRACT FROM AUTHOR]

We present the results of studying electronic, elastic, vibrational, and thermodynamic properties of type-VIII clathrates Ba8Ga16Sn30 Ba8Al16Sn30 calculated from a first-principles approach. The calculations utilize the generalized gradient approximation to density functional theory. The results indicate that the Ba8Ga16Sn30 and Ba8Al16Sn30 are indirect semiconductors with fundamental band gaps of 160 meV and 315 meV, respectively. It was also found that the stiffness of Al containing type-VIII clathrate does not show any significant change against the uniform pressure, shearing, and linear strains. The phonon spectrum and the phonon state densities of these compounds as well as the Raman and infrared active modes were further calculated and the effects of replacing the Ga with Al atoms on the properties of interest were discussed. The calculated elastic, vibrational, and thermodynamic properties along with Raman and IR spectra are reported for the first time. The identification of the Raman and infrared active modes will be especially useful for the experimental characterizations of these compounds. Our calculations show that the heat capacities of these clathrates increase smoothly with temperature and approach the Dulong-Petit value at about room temperature, which agrees with the existing experimental data. [ABSTRACT FROM AUTHOR]

The lattice dynamic, elastic, superconducting, and thermodynamic properties of the high-pressure cubic metallic phase AlH3 are studied within density function theory. The calculated elastic modulus and phonon dispersion curves at various pressures indicate that the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature was calculated using Allen-Dynes modification of the McMillan formula based on the Bardeen-Cooper-Schrieffer theory. It is found that Tc approaches a linear decrease in the low pressure range at the rate dTC/dP≈-0.22 K/GPa but gradually decreases exponentially at higher pressure, and then it becomes 0 K upon further compression. The calculations indicate that Tc is about 2.042 K at 110 GPa, in agreement with experimental results. The soft phonon modes, especially the lowest acoustic mode, contribute almost 79% to the total electron-phonon coupling parameter sλ for cubic AlH3 at 73 GPa. However, they disappear gradually with increasing pressure, showing a responsibility for the variation of Tc. The thermodynamic properties of cubic AlH3, such as the dependence of thermal expansion coefficient αV on pressure and temperature, the specific heat capacity CP, as well as the electronic specific heat coefficient Cel, were also investigated by the quasi-harmonic approximation theory. [ABSTRACT FROM AUTHOR]

We report on a triclinic unit cell deformation of fully strained InGaN layers grown on vicinal GaN (00.1) substrates. The samples were examined using the high-resolution X-ray diffraction (HR XRD) using a set of asymmetrical reflections and one symmetrical reflection of 00.2. The substrate miscut induced triclinic deformation of the layer unit cells, breaking the hexagonal symmetry. The experimental results are compared with predictions of the theory of elasticity. We formulate equations for unit cell parameters of layers grown on substrates cut in any direction, based on the equations given by Romanov et al. [J. Appl. Phys. 100, 023522 (2006)]. Additionally, the paper provides a recipe of the XRD measurements necessary to establish unit cell parameters (useful for composition determination of ternary compounds) of the hexagonal mismatched layers grown on off-axis substrates. [ABSTRACT FROM AUTHOR]

A correction to the article "Pump and probe waves in dynamic acousto-elasticity: Comprehensive description and comparison with nonlinear elastic theories," by G. Renaud and colleagues published in a 2013 issue of the "Journal of Applied Physics" is presented.

The thermal-electro-mechanical behavior of second generation YBa2Cu3O7-δ coated conductors subjected to thermal cooling and electric charging is investigated in this paper. Shear stress at the interface and transverse normal stress in the film are analyzed through the elasticity theory. The plane strain approach is assumed, and a singular integral equation governing the problem is derived in terms of the interfacial shear stress, thermal strain, and the electromagnetic force. After that, we evaluate the shear and transverse stress distribution in the conductor during cool down and electric charging, respectively. The results show that large residual compressive stress (about 150 MPa) and interfacial shear stress (about 400 MPa) remain in the conductor during cool down. In the electric charging process while small compared to the thermal one destructive tensile stress present near the edges of the conductor. Effects of the stiffness of substrate on the stress distribution in the conductor are investigated also. [ABSTRACT FROM AUTHOR]

Bond stretching and angle bending force fields, appropriate to describe in-plane properties of graphene sheets, are derived using first principles' methods. The obtained force fields are fitted by analytical anharmonic potential energy functions, providing efficient means of calculations in molecular mechanics simulations. Using both molecular dynamics simulations and first principles' methods, numerical results regarding the mechanical behavior of graphene monolayers under various loads, like uniaxial tension in different directions or hydrostatic tension, are presented and compared. Graphene's response in shear stress is also investigated using molecular dynamics, where a noticeable asymmetric mechanical behavior is found. Stress-strain curves and elastic constants, such as, Young modulus, Poisson's ratio, bulk modulus, and shear modulus, are calculated. Our results are compared with available experimental estimates, as well as, with corresponding theoretical calculations. Finally, the effects of the anharmonicity of the extracted bond stretching and angle bending potentials on the mechanical properties of graphene are discussed. [ABSTRACT FROM AUTHOR]

In this work, we focus on the study of the structural and elastic properties of mercury digallium selenide (HgGa2Se4) which belongs to the family of AB2X4 ordered-vacancy compounds with tetragonal defect chalcopyrite structure. We have carried out high-pressure x-ray diffraction measurements up to 13.2 GPa. Our measurements have been complemented and compared with total-energy ab initio calculations. The equation of state and the axial compressibilities for the low-pressure phase of HgGa2Se4 have been experimentally and theoretically determined and compared to other related ordered-vacancy compounds. The theoretical cation-anion and vacancy-anion distances in HgGa2Se4 have been determined. The internal distance compressibility in HgGa2Se4 has been compared with those that occur in binary HgSe and [variant_greek_epsilon]-GaSe compounds. It has been found that the Hg-Se and Ga-Se bonds behave in a similar way in the three compounds. It has also been found that bulk compressibility of the compounds decreases following the sequence '[variant_greek_epsilon]-GaSe > HgGa2Se4 > HgSe.' Finally, we have studied the pressure dependence of the theoretical elastic constants and elastic moduli of HgGa2Se4. Our calculations report that the low-pressure phase of HgGa2Se4 becomes mechanically unstable above 13.3 GPa. [ABSTRACT FROM AUTHOR]

A correction to the article "First-principles Study of Elastic Properties of Cubic Cr1-xAlxN alloys," published in a previous issue of the "Journal of Applied Physics," is presented.

The elastic properties of paramagnetic cubic B1 (c-) Cr1-xAlxN ternary alloys are studied using stress-strain and energy-strain methods within the framework of density functional theory. A strong compositional dependence of the elastic properties is predicted. Young's modulus, E, and shear modulus, G, exhibit the same compositional trends as experimentally measured hardness values (i.e., increasing with Al content), while bulk modulus, B, remains almost constant. The isotropic elastic response in the c-Cr1-xAlxN is predicted for concentrations around x = 0.50. Brittle behavior and directional bonding characteristics are predominant in the c-Cr1-xAlxN coatings in the whole composition range and become more pronounced with increasing Al content. [ABSTRACT FROM AUTHOR]

Ultrasonic measurements allow non-destructive evaluation of mechanical properties of wood. However, it is unclear how these ultrasonically determined properties relate to comparable values obtained by traditional mechanical experiments, e.g., three point bending performed at different probing frequencies. In addition, although a link between the modulus of rupture (MOR) and the modulus of elasticity (MOE) obtained with static methods is established, little research exists on the correlation between the ultrasonically determined dynamic elastic modulus and MOR. Therefore, we set out to link the modulus values obtained by three-point bending to those obtained by ultrasonic measurements at different frequencies. We compared the modalities using a fractional derivative model that theoretically predicts a frequency dependency of the dynamic elastic modulus. We determined MOE and MOR in 102 Norway Spruce samples (340 to 510 kg/m3 density) by three-point bending followed by ultrasonic through-transmission measurements that quantified the dynamic modulus at 500 kHz, 4 MHz, and 8 MHz. This is the first report on such a frequency series for Norway Spruce. Our results provide a conversion factor that permits comparing ultrasonically and statically measured MOE values. Depending on the ultrasonic frequency, correlations ranging from 0.3 to 0.53 between the ultrasonic dynamic modulus and MOR were found. [ABSTRACT FROM AUTHOR]

The physical mechanism of recoil hysteresis loops has been subject to dispute in recent years. This paper deals with the origin of recoil hysteresis in nanocomposite Pr8Fe87B5 magnets. It is shown by investigating the recoil loops and magnetic activation of melt-spun ribbon of Pr8Fe87B5 at different temperatures that the openness of recoil hysteresis loops is strongly dependent on the magnetic activation as the negative field (opposite to magnetization) is cycled to zero in a remanent state. The hysteresis of recoil loops originates from the reversible magnetization reversal of hard phase, which is probably caused by the energy of isotropic exchange coupling overcoming the energy barrier of magnetocrystalline anisotropy. So, the hysteresis is codetermined by the exchange coupling and variation of anisotropy, thus the openness has a linear relationship with the product of magnetic moments of activation and reversible susceptibility. [ABSTRACT FROM AUTHOR]

Due to its high feature resolution and the capability to produce 3D-structures without the need of support-structures, two-photon polymerization (2PP) is one of the fastest growing technologies in the field of additive manufacturing. To ensure good quality of the fabricated parts, proper methods for evaluating the suitability of different material systems for 2PP are necessary. In this paper, we present a fast screening method based on measuring the Young's modulus of micro-cantilevers giving a quantifiable measure and representing the material- and fabrication-properties in one experiment. [ABSTRACT FROM AUTHOR]

Density-functional calculations are performed to explore the relationship between the work function and Young's modulus of RhSi, and to estimate the p-Schottky-barrier height (SBH) at the Si/RhSi(010) interface. It is shown that the Young's modulus and the workfunction of RhSi satisfy the generic sextic relation, proposed recently for elemental metals. The calculated p-SBH at the Si/RhSi interface is found to differ only by 0.04 eV in opposite limits, viz., no-pinning and strong pinning. We find that the p-SBH is reduced as much as by 0.28 eV due to vacancies at the interface. [ABSTRACT FROM AUTHOR]

First principles calculations have been carried out to analyze structural, elastic, and dynamic stability, of CdO under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type (B2) structures determined as a function of compression suggests the B1 → B2 transition at ∼87 GPa, in good agreement with experimental value of 90.6 GPa [Liu et al. Phys. Rev. B 70, 0941141 (2004)]. Various physical quantities, such as zero pressure equilibrium volume, bulk modulus, pressure derivative of bulk modulus, Gruneisen parameter, and Debye temperature have been derived from the theoretically determined equation of state. All these physical quantities show a reasonably good agreement with the available experimental data. Additionally, employing the theoretically determined thermal equation of state in conjunction with Rankine Hugoniot relation, we have predicted the Hugoniot of B1 phase of this material. The single crystal elastic constants of B1 phase calculated up to the pressure of 166 GPa show that though, the shear elastic stability of B1 phase decreases monotonically with compression, it still remains stable elastically even at transition point. Our lattice dynamic calculations show that the B1 phase remains stable dynamically also for pressures <118 GPa. For B2 phase, our calculations demonstrate that this structure will be elastically stable beyond ∼38 GPa. However, to stabilize this phase dynamically a still higher pressure of ∼55 GPa will be required, which is less than B1 → B2 transition pressure. [ABSTRACT FROM AUTHOR]

In a previous publication [J. Appl. Phys. 110, 036103 (2011)], we have shown that the bulk expansivity and elastic data can reproduce the self-diffusion coefficients in MgO over a wide range of values, i.e., 20 orders of magnitude. This publication was crossed with recent studies supporting the view that the Anderson-Gruneisen parameter δ is independent of the temperature in alkaline earth oxides. Here, we take this view and using the resulting elastic and expansivity parameters, we repeat the calculation for the diffusion coefficient of O in MgO. The results obtained agree with the experimental data. [ABSTRACT FROM AUTHOR]

In the framework of coupling surface/interface theory, a self-consistent scheme of effective field method is proposed to solve the dynamic electro-elastic properties of piezoelectric nanocomposites. The piezoelectric matrix with randomly distributed piezoelectric nano-fibers is reduced to the problem of an effective piezoelectric medium with a typical piezoelectric nano-fiber. The effective wave number and piezoelectrically stiffened elastic modulus are obtained on the basis of the derived imperfect interface conditions around the piezoelectric nano-fiber. Analyses show that the energy at the surface/interface shows significant effect on the dynamic electro-elastic properties, and the effect under different incident frequencies is discussed in details. [ABSTRACT FROM AUTHOR]

Flat, low-stress, boron-doped polysilicon thin films were prepared on crystalline silicon substrates by low pressure chemical vapor deposition. The films' surface morphologies and internal stresses were investigated using scanning probe microscope and AFM-Raman, respectively. The elastic modulus (E) was measured along with the hardness (H) using the nanoindentation technique. It was found that films deposited at the highest temperature had the largest grain size and surface roughness. The internal stresses in the films are tensile stresses, which are not uniform over the surfaces and present the gradient distribution along the thickness. Both the surface roughness and the internal stresses affect the nanoindentation tests. The tensile stresses in the films give extra forces to the diamond indenter, so the depths of penetration should be larger than those obtained from the films with stress free for a given load, which leads to an underestimation of E as well as H. But under the applied conditions, the increasing surface roughness can not only lead to the reductions of depths of penetration but also cause the measurement values of E and H to be more dispersive and uncertain. So for a given load, if the maximum depth of penetration in the rough surface is smaller than that in the smooth surface, the surface roughness is the main factor affecting the nanoindentation tests. On the contrary, the tensile stress is the main factor. [ABSTRACT FROM AUTHOR]

We investigated the effects of interfacial bonding on the mechanical properties in the Si-carbon nanotube (CNT) nanocomposite by a molecular dynamics approach. To describe the system appropriately, we used a hybrid potential that includes Tersoff, AIREBO (adaptive intermolecular reactive empirical bond order), and Lennard-Jones potentials. With increasing bonding strength at the interface of Si matrix and CNT, toughness as well as Young's modulus and maximum strength increased steadily. CNT pull-out and load transfer on the strong CNT were identified as the main mechanisms for the enhanced properties. At optimum bonding, crack tip was deflected around CNT and the fracture proceeded in plastic mode through Si matrix owing to the strong reinforcement of CNT, and resulted in a further enhancement of toughness. At maximum bonding, however, only load transfer is operative and the fracture returned to brittle mode. We concluded that a strong interface as long as the CNT maintains its structural integrity is desirable to realize the optimum result. [ABSTRACT FROM AUTHOR]

We present an analytical model to relate the elastic properties of crystalline polyethylene based on a molecular mechanics approach. Along the polymer chains direction, the united-atom (UA) CH2-CH2 bond stretching, angle bending potentials are replaced with equivalent Euler-Bernoulli beams. Between any two polymer chains, the explicit formulae are derived for the van der Waals interaction represented by the linear springs of different stiffness. Then, the nine independent elastic constants are evaluated systematically using the formulae. The analytical model is finally validated by present united-atom molecular dynamics (MD) simulations and against available all-atom molecular dynamics results in the literature. The established analytical model provides an efficient route for mechanical characterization of crystalline polymers and related materials. [ABSTRACT FROM AUTHOR]

We have investigated the relationship between in-plane strain and optical polarization in AlGaN epitaxial layers as a function of Al content and of Si concentration. Al content and in-plane strain were measured by reciprocal space mapping using a simple relationship from the tensor of elastic moduli. The change of valence band energy separation based on the measured in-plane strain was in good agreement with the change of polarization degree as a function of Al content. The dependence of polarization degree on Si concentration was also explained by the change of in-plane strain, and polarization switching occurred around the Al content and strain as calculated by the k · p approach with the cubic approximation. [ABSTRACT FROM AUTHOR]

The acoustic properties and their pressure dependence have been determined to 18.5 GPa for nearly amorphous poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800) using high-pressure Brillouin scattering. At all measured pressures, both longitudinal and transverse acoustic modes were observed allowing for calculation of the pressure-volume isotherm for this predominantly amorphous material. Analysis of the room temperature isotherm using semi-empirical equation of state fitting forms to 5.5 GPa yielded a zero-pressure bulk modulus, Ko, and pressure derivative, Ko′, of 2.8 GPa and 30.6, respectively, which are consistent with the results from dilatometry measurements at very low pressures. Furthermore, the C11 and C12 elastic moduli for the isotropic polymer were determined at each pressure interval and, subsequently, examined to provide the pressure dependence of the bulk, shear, and Young's moduli. These results are discussed in relation to polymer mechanics at pressures far exceeding those of previous, static compression experiments. [ABSTRACT FROM AUTHOR]

The study of the properties of the defects provides an effective way to control the physical properties of solids, such as conductivity. Using a thermodynamic model which correlates the activation Gibbs energy with the bulk elastic and expansivity data, we determine the activation volumes for the conduction processes for ZnO. The calculated activation volumes are in agreement with their experimental values. [ABSTRACT FROM AUTHOR]

Using newly developed particle swarm optimization algorithm on crystal structural prediction, we first predicted that MoB2 undergoes a phase transition from the low-pressure rhombohedral phase to a tetragonal α-ThSi2-type phase with a volume drop of 4.01% when the applied pressure is 68 GPa. Phonon calculations suggest the α-ThSi2-type phase can be quenchable to ambient pressure. Then, Young's modulus E and shear modulus G as a function of crystal orientation for the α-ThSi2-MoB2 have been systematically investigated. Further mechanical properties demonstrated that α-ThSi2-MoB2 possesses large bulk modulus of 322.3 GPa and high Vickers hardness of 32.1 GPa, exceeding the hardness of α-SiO2 (30.6 GPa) and β-Si3N4 (30.3 GPa). The excellent mechanical properties are attributed to the three-dimensional networks linked by strong covalent B-B bonding and Mo-B covalent bonds in MoB12 polyhedrons. [ABSTRACT FROM AUTHOR]

Recently, substantial efforts have been focused on the efficiency enhancement of vector Preisach-type model implementation methodologies. This paper presents a computationally efficient approach for implementing a vector Preisach-type hysteresis model through an ensemble of octal clusters of coupled step functions. Within this approach, each cluster can be tuned by proper selection of coupling factors to exhibit vector hysteresis properties, thus minimizing number of clusters needed to construct a vector Preisach-type model. [ABSTRACT FROM AUTHOR]

In this paper, we present a model for temperature dependent hysteretic nonlinearities with nonlocal memories. This model can be applied to describe hysteretic material behavior. Common applications are ferromagnetic or magnetostrictive materials. Our model consists mainly of a Preisach operator with a continuous Preisach weight function. We choose a weight function which shows a strong correlation between the function's parameters and certain properties of the hysteresis curve. As a new approach, the weight function is written as a function of temperature. The model parameters are customized to a set of symmetric hysteresis curves. We verify our model for magnetic materials with differently shaped hysteresis curves, different temperatures and magnetic field amplitudes. [ABSTRACT FROM AUTHOR]

There is great interest in using proximal probe techniques to simultaneously image and measure physical properties of surfaces with nanoscale spatial resolution. In this regard, there have been recent innovations in generating time-resolved force interaction between the tip and surface during regular operation of tapping mode atomic force microscopy (TMAFM). These tip/sample forces can be used to measure physical material properties of surface in an analogous fashion to the well-established static force curve experiment. Since its inception, it has been recognized that operation of TMAFM in fluids differs significantly from that in air, with one of the major differences manifested in the quality factor (Q) of the cantilever. In air, Q is normally on the order of 200–400, whereas in fluids, it is of the order of approximately 1–5. In this study, we explore the impact of imaging parameters, i.e., set point ratio and free cantilever oscillation amplitude, on time varying tip-sample force interactions in fluid TMAFM via simulation and experiment. The numerical AFM model contains a feedback loop, allowing for the simulation of the entire scanning process. In this way, we explore the impact of varying the Young’s modulus of the surface on the maximum tapping force. [ABSTRACT FROM AUTHOR]

The article presents the author's response to comments on his article "Free transverse vibration of the fluid-conveying single-walled carbon nanotube using nonlocal elastic theory." It states Eringen's theory of nonlocal elasticity was based on the mechanics of solids and with a nonlocal constant is used to modify the elasticity theory, while being limited to devices on the nanometer scale. It mentions that nonlocal effects on the mechanical behaviors of nanostructures is difficult to validate.

A modified atomic force microscopy (AFM) system, based on a force modulation technique, has been used to find an approximate value for the elastic modulus of a single peptide molecule directly from a mechanical test. For this purpose a self-assembled monolayer built from two kinds of peptides, reactive (able to anchor to the AFM tip) and nonreactive, was synthesized. In a typical experiment a single C[sub 3]K[sub 30]C (C=cysteine, K=lysine) peptide molecule was stretched between a Au(111) substrate and the gold-coated tip of an AFM cantilever to which it was attached via gold–sulfur bonds. The amplitude of the cantilever oscillations, due to an external force applied via a magnetic particle to the cantilever, was recorded by a lock-in amplifier and recalculated into stiffness of the stretched molecule. A longitudinal Young’s modulus for the α-helix of a single peptide molecule and for the elongated state of this molecule has been estimated. The obtained values; 1.2±0.3 and 50±15 GPa, for the peptide α-helix and elongated peptide backbone, respectively, seem to be reasonable comparing them to the Young’s modulus of protein crystals and linear organic polymers. We believe this research opens up a means by which scientists can perform quantitative studies of the elastic properties of single molecule, especially of biologically important polymers like peptides or DNA. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin amorphous films of ZrB[sub 3] grown on Si(111) substrates by chemical-vapor deposition are, upon annealing at 960 °C, transformed to films composed of nanocrystallites (6-10 nm extent) with a nominal composition of Zr[sub 0.9]Si[sub 0.3]B[sub 3]. The independent elastic constants of the layers are determined from the dispersion of the surface and pseudo-Sezawa acoustic excitations and reveal large enhancements in the C[sub 11] and C[sub 44] constants accompanying the conversion of ZrB[sub 3] to the nanocrystalline phase. Since the transverse sound velocities of the binary and Zr[sub 0.9]Si[sub 0.3]B[sub 3] are in near resonance with the sound velocity of Si (V[sub T][sup Si]=4.8 km/s), only the Rayleigh surface wave is localized to the film while all higher-order acoustic modes are evanescent. Despite the strong decay channels, high-lying excitations with velocities as large as 25 km/s (>V[sub T][sup Si]) are observed in Brillouin light scattering. Insight into these acoustic properties is provided by evaluating the elastodynamic Green's functions and associated acoustic-mode densities. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]